Use ActiveRecord::Base for connection info

Not ApplicationRecord, since it might not be defined, and
ActiveRecord::Base.connection is what is used everywhere else in this
class.

lib/evm_database.rb

@@ -103,7 +103,7 @@ def self.local?
   end
 
   # Determines the average time to the database in milliseconds
-  def self.ping(connection = ApplicationRecord.connection)
+  def self.ping(connection = ActiveRecord::Base.connection)
     query = "SELECT 1"
     Benchmark.realtime { 10.times { connection.select_value(query) } } / 10 * 1000
   end